Flexible Armor: Mysterious Seahorse Astounds Scientists

Sea horses get their exceptional flexibility from the structure of their bony plates, which form its armor. The plates slide past each other. Here the seahorse's skeleton, as well as the bony plates, are shown though a micro CT-scan of the animal.

The curious seahorse, a tiny fish that swims in a vertical position and looks a lot like a miniature horse, has astounded researchers by its ability to withstand crushing forces that would destroy nearly every other living creature.

And it just may help the researchers borrow from the world of biology to solve some really tough problems in the world of engineering.

The seahorse is the latest in a growing list of organisms in the relatively new field of biomimetics. If you are trying to solve an engineering problem, find something in nature that has already done it, then steal its secrets.

Engineers at the Jacobs School of Engineering at the University of California, San Diego, have been studying several animals to see how they protect themselves.

Their goal is to develop a device that can grab an object, even something deep under the sea, while withstanding the forces of nature and the threats from predators.

The engineers looked at all sorts of critters, including a large fish that survives in the piranha-infested waters of Brazil's Amazon forest, and is protected by a layer of armor that is more than a match for the razor-sharp teeth of the piranha.

But you can't pick up something with the body of a fish, so they turned elsewhere.

"We started out looking at antlers, and horns, as defense, then we went on to the armadillo and turtle shells, as armor," materials science professor Joanna McKittrick of UCSD said in a telephone interview. But what they needed was a truly remarkable creature, and the seahorse stepped up to the plate.

"The seahorse was a natural," Mckittrick said. The research, led by McKittrick and fellow materials science professor Marc A. Meyers, was published in the journal Acta Biomaterialia, and it describes seahorses like this:

"They have a head like a horse, a long tubular snout like an anteater, eyes that move independently like a chameleon, a brood pouch like a kangaroo, camouflage skin like a flounder, and a flexible prehensile tail like that of a monkey."

That sounds like an animal designed by a committee that wasn't entirely sure what it wanted to do. But as the researchers subjected dead seahorses to forces powerful enough to compress their body to half their normal size, they found something extraordinary. That amount of compression, which would kill just about anything else, except a sponge, did no discernible damage to the seahorse.

McKittrick said that when she saw the fish's ability to withstand that, she was "bamboozled." That's an engineering term for stunned, or astonished, or really surprised.

The researchers found that the seahorse's vertebra, which runs the length of its body, is protected by a series of "bony plates" that slide past each other during compression.

But Michael Porter, a doctoral student who conducted most of the lab work and is lead author of the study, said in a telephone interview that the finding was surprising because bone would be expected to crack, and then shatter under such compression. That's because bones are made mostly from minerals and are brittle.